Solid state imagers, including charge coupled devices (CCD) and CMOS sensors, are used in photo imaging applications. A solid state imager includes a focal plane array of pixels, each one of the pixels including a photosensor having a region for accumulating photo-generated charge. Micro-lenses are placed over the imager pixels and are used to focus light onto their respective photosensors. The use of micro-lenses significantly improves the photosensitivity of the imager by collecting light from a large light collecting area and focusing it on a small photosensitive area of the pixel. The ratio of the light collecting area to the overall area of the pixel is known as the “fill factor” of the pixel.
Optimally, all of the light from a pixel's microlens will be directed to the pixel's photosensitive area. However, in practice, a phenomenon known as crosstalk can result when off-axis light strikes a micro-lens at an obtuse angle and strikes the photosensitive region of an adjacent pixel. Crosstalk can degrade the quality of a captured image by causing a light reading that is too low in some pixels and too high in others.
Accordingly, it is desirable to have a lens that could significantly reduce crosstalk and improve the efficiency of a pixel.